Optical and opto-electronic components produced with a silicon-based technology are key components, for example for optical telecommunications or for optical connections within or between microelectronics circuits. Examples of such components are couplers, waveguides, modulators and photodetectors, in particular.
Modern photodetectors use germanium as a detector material due to its significantly better absorbance compared to silicon in the wavelength range used for optical communication (1.3-1.6 μm). A “PIN diode” (“P” standing for p-doped region, “I” for intrinsic region and “N” for n-doped region) is often used as a detector. Important parameters of the diode are dark current, photocurrent, sensitivity and optical bandwidth. Very fast Ge photodiodes with an intrinsic region width of a few hundred nanometers and with an optical bandwidth of 50 GHz have already been demonstrated.
Such diodes are typically produced by epitaxial growth directly on an SOI substrate, which allows direct coupling of the detector to the waveguide made from the upper monocrystalline Si layer of the SOI structure. The light to be detected can thus be supplied laterally to the diode, which allows the diode to be independently optimized with regard to sensitivity and optical bandwidth.